This invention relates to the field of multiple phase filter cartridges. More particularly, this invention relates to the field of multiple phase filters of the cartridge type having two or more distinct filtering layers, at least one of which contains an active filtering material, the active filtering material preferably being in a pulverized form.
The advantages of the use of active particles for use in filtration and treatment, chemical or otherwise, has long been recognized in the filter art. In particular, the theoretical advantages of the use of such active materials in extremely fine or pulverized form, i.e., 40 mesh size or smaller, has also long been recognized but has found little practical application. A particular problem has been recognized in that when a bed of active powder of less than 40 mesh size is used alone, the fluid dynamics of the material flowing through the filter cause the fine powder to "channel," i.e. passages are formed through the bed of fine active powder. The formation of these passages serves, in effect, to allow the fluid to become untreated as it passes through the channels without contact with the active powder. It has been proposed to add resinous binders with the pulverized active material to form a structure of suitable physical integrity whereby the channeling will be avoided. However, the amount of resinous binder required to achieve the desired physical integrity is usually sufficient to partially seal off the pores of the active powder, thus seriously affecting performance of the filter.
Other efforts to employ active materials have involved grannular materials of greater than 40 mesh size bonded together with various resinous materials to form desired shapes, but such filters have the decided disadvantage of low permeability and little filtration in depth. Similarly, other specifically shaped products are available which are composed of coarse granules or pelletized particles of active material bonded together with various resinous materials. Although these further products offer some permeability to fluid flow, they serve as screens, in effect, for particle removal from the fluid flow, and seal off rapidly during the filtration cycle. In addition, because of the greater than 40 mesh screen size of the granules or pellets, the full effect of the surface area that would otherwise be available with pulverized, fine active powder is lost.
Filter cartridges are, of course, in general use which incorporate various combinations of pleated and non-pleated filtration media, i.e. paper, cloth, felt, etc. along with granular active materials such as activated carbon and ion exchange resins. In almost every case, some type of fine porous medium is employed downstream from the granular material to retain the granular active material as well as the fine active particles which break loose by fluid dynamic attrition. Such "fines" would be a source of contamination to the resulting filtrate. Although such filters can be designed to provide for a combination of physical filtration and chemical treatment, none are known which effectively take advantage of the considerably greater surface area of pulverized rather than granular or pelletized active material such as activated carbon, molecular sieves, and ion exchange resins.